Method for protection of circuits in water-cooled generators

FIELD: electrical engineering.

SUBSTANCE: in water-cooled generator, gas is extracted in N points from generator volume, and measurement of humidity in all points of extraction, according to invention, is carried out with single metre of moisture concentration serially, value of humidity in N extraction point of knowingly driest gas is subtracted from results of current measurements in N-1 point of sample extraction, and speed of differential data variation is used to identify emergency water leaks.

EFFECT: invention provides for detection of emergency mode in water-cooled generators related to water leaks, reduced time required for detection of emergency mode.

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The invention relates to the technological control of power generators and can be used in power plants to protect from moisture isolation of electrical circuits of the generators.

In the powerful electric generators produces a large quantity of thermal energy (of the order of 250 kW per cubic meter of active volume of the machine), leading to a rise in temperature up to values exceeding the permissible during long-term operation of the elements of the generators (usually not higher than 110°C) [1, str, 319]. To maintain the temperature in the volume of generators used in the cooling system. Modern generators large power systems are used for the cooling of two types [2, section 6]:

- hydrogen-water,

with full water cooling.

In the first case, the cooling water is pumped through the hollow conductors of the stator winding and the rotor and the metal parts are cooled blown through special channels by hydrogen. Such systems are typical for turbo-generators with capacity from 60 to 360 MW.

In systems of the second type of water pumped through the conductors of the stator, the rotor and the special bonds of steel tube active stator are cooled all the elements of the generator. Protection insulation of the windings from moisture is provided by blowing dried air active volume of the generator. Under the basic system characteristic of the turbo-generators with a capacity of 800 MW and more.

A great danger to the health of the generators is moisture insulation of the windings of the stator and rotor, leading to short circuits with catastrophic destruction of the generators [3, 15, 38, 65-68]. The probability of such events could be reduced by passing a cooling gas, which over time increases the concentration of water vapor through the desiccant. Thus, the cooling system includes a source of clean, dry gas to fuel gas generator), gas dehydration, gas cooler, intake fans, piping with shutoff valve [4, p.42-47].

However, the presence of a desiccant gas does not exclude moisture insulation of the windings. This is due to two groups of reasons [4, p.57]. The first group of causes leads to a slow increase in the concentration of water vapor: the failure of the refrigerating machine in the gas drying system, fan failure, or the gas valve. When such failures do not need emergency output the generator operating mode. Enough to increase the recharge oscillator with dry gas or attach a backup drier gas.

The second group of reasons is connected with the water leaks from the ducts of the stator, rotor, inlet hoses, seals or gas cooler. In such cases it is necessary to bring the generator operating mode for the minimum time and to block the flow in the s before as will begin intensive moisturizing elements of the generator (emergency mode).

The known method of relay protection circuit generator voltage generator-transformer with direct water cooling and device for its implementation by the RF patent №2066910 [5]. According to the method on the circuit generator voltage impose alternating currents of two frequencies and determine the equivalent active conductivity of the insulation and cooling medium, and tangent of dielectric loss angle. The data and develop the team off, if at least one of these parameters exceeds the allowable value.

The method has two major drawbacks: low speed and high accuracy. The first drawback stems from the fact that the insulation resistance and the loss tangent is functionally associated with the hydration of isolation, and it is very inertial process. The second drawback associated with the variability of the parameters of the insulation and the cooling water in the normal mode of operation of the generator. According to [2, paragraph 4.12] the insulation resistance should be not less than 10 Megohms per kilovolt voltage winding at a temperature of 30°C and it can be reduced in two times when the temperature is 20°C; similarly for water [4, paragraph 6.12] the specific resistance should be not less than 2000 Ohm·m when the tempo is the atur 25°C and allowed to change up to 500 Ohm·m

The closest technical solution is the system of measurement of the concentration of moisture in the generator with full water cooling TSV - 800 - 2UZ described in section 16 "Ventilation and drying gas turbine generator" operating Instructions TSV - 800 - 2UZ [6, p.51-59]. According to [6] the air in the generator circulates in a closed circuit: dry air is sucked into the fan and under the pressure of 10 to 30 mm of water column is directed to the Central part of the generator. The air flows in both directions from the center to the front parts of the generator of the turbine and exciter), where he is already saturated with moisture, is fed into the drying gas. After the desiccant dry air enters the fan described above.

For controlling the concentration of moisture in the working volume of the generator set 7 knots of air samples: one at the outlet fan (air dry) and three nodes in the frontal parts of the generator. To nodes in the selection connected hygrometers "Wave - 2M". When reaching the testimony humidity 20°C, dew point and above the generator must be disconnected from the mains for 5 minutes [6, paragraph 4.9.23].

Moisture measurement gas more dynamic method than measuring humidity insulation of the windings, since the moisture is distributed in the volume of the generator due to the forced diffusion, defined by the rate of gas flow fans. However, in the description of the technical solution, there are two significant drawbacks.

The first drawback. Low accuracy of measurement of the concentration of moisture. First of all it is connected with the instability of the metrological characteristics of the sensors, convert the concentration of water vapor in the parameter of an electrical signal and, secondly, the dependence of the hygrometer from thermodynamic state of the gas (temperature, pressure)surrounding the sensor. As a rule, near the humidity sensor is placed a resistance thermometer according to the testimony which introduce the necessary amendments in the humidity measurement result. But this is done with the measurement error of the temperature and the pressure is generally not measured.

The second drawback. The diagram and the set of running it operations does not allow to distinguish the nature of the limit values of concentration of vapor in the gas - was it for reasons of the first group (not requiring output of the generator from the working mode) or the second (emergency mode).

The technical problem solved by the invention is the identification emergency mode for generators with water cooling associated with water leaks and reducing the time of its discovery. This object is achieved in that the generator with water cooling in N points produce gas from the volume of the generator, and humidity measurement in all sampling points, according to the invention, the OS is p one measure of the concentration of moisture in series, from the results of the current measurements in the N-1 sampling point is deducted from the value of the humidity in the N-th point selection obviously most of the dry gas and the rate of change of the differential data is judged emergency water leaks.

Consider the implementation of the method on the example outlined above turbine generator TSV - 800 - 2UZ. All 7 points of sampling are connected through a gas switch to one moisture meter. Switches can be gas switch or set of 7 pneumatic relay. However, in this particular case, given the low excess air pressure in the volume of the generator, it is advisable to use the boosters of consumption; they allow to reduce the time of passage of air from the point of sampling to measure moisture. The sequence of inclusion precursors flow and measuring humidity controls microprocessor node that can perform advanced computational procedures or transmit the measurement results to the computer.

The device operates as follows. In the first cycle of measurements (n=1, where n is the cycle number) are derived humidity values 7 sampling points:

where Fi- the humidity value of the first sampling point (i=1, 2,..., N=7), the number in brackets indicates the number of the measurement cycle.

In the second cycle of measurements, done the subject through a known time interval Δt, will the results of the measurements:

Among all sampling points, there is one dedicated, characterized in that the humidity of the gas in the zone selection is minimal. This is the point, which is located behind the fan forcing dry gas. Let us assign to her room n

According to the invention then calculates the difference:

Next, calculate the velocity V1-2changes in the differential data, change the increments humidity values belong to the interval Δt:

Write V1-2(i) means that the rate of increase of the concentration of moisture corresponds to the i-th sampling point; the calculations are performed according to the measurement results in the first and second cycles. In the next cycle of measurement formulas(3), (4), (5) obtains the value of the rate of change of the concentration of moisture V2-3(i) and so on in each cycle to n, after which you will receive the value of the velocity Vn-1-n(i). The values of the rate-of-rise vlagosoderzhaniya gas identify the nature of the process of increasing the concentration of moisture in it (the failure of the gas system or emergency water leakage in the case of the generator).

Consider two numerical examples illustrating the capabilities of the proposed protection method.

Suppose, on the Azania hygrometer in several sampling points were close to the maximum permissible values (15°C dew point), and slew rate concentration is low, for example, of 0.05°C and dew point in a minute. This means, according to (5), dry gas (at the point of selecting the number N) wetland. Conclusion: out of order one of the elements of the system of the drying gas. Although the concentration of moisture in the gas is high, there is no need emergency output of the turbogenerator. It is enough to determine the failed element (dehumidifier, fan and replace it with the backup.

The second case. Concentrations of moisture in the sampling points i, i+1 equal to 4°C and dew point, but the concentration is increasing at a rate of 0.5°C dew point in a minute. This speed increase of the concentration of moisture indicates the presence of a leak of water (for example, in one of the frontal parts of the generator), which is converted into the vapor phase. Although the absolute value of the concentration of moisture is very far from the limit value 15°C dew point, the system must issue the alarm.

The sequence of switching points of the gas in the loop can be any, but preferably each cycle to start with point selection knowingly dry gas. This eliminates the need to store in the memory of the microprocessor, the results of measurements of the concentration of moisture in the other points, because the difference between (3), (4) and speed (5) are calculated immediately upon receipt of the measurement results from other sampling points of gas.

For the adoption of achieving the invention the objectives define the error of the differences of the concentrations of moisture, calculated by expressions (3) and (4). In General, consider the error δ [∆Fk(i)] a difference for the k-th point of the gas in the i-th cycle:

The values included in the expression (6) measurements consist of the true values of the measured variables (Fk0(i) and FN0(i) respectively), the systematic component of the error (θkand θNrespectively) and random components εkand εN. Considering the above-mentioned expression (6) can be written in the form:

δ [∆Fk(i)]=δ[Fk0(i)FN0(i)+θkNkN].

Because, according to the invention, measurement is performed by one measuring channel, the systematic component of error in all measurements is constant, i.e. θkNand their difference is equal to zero. Therefore

and the error difference will be only random component of the error, the feature of which is the standard deviation σ [∆Fk(i)]. To determine pre-calculate the variance of the expression (7):

D [∆Fk(i)]=D[Fk0(i)FN0(i)+εkN]= D[Fk0(i)FN0(i)]+D[εkN].

Variance the difference between Fk0(i) FN0(i)as a constant number equal to zero; it's an expression that is converted to the attribute of thesis the version of the sum (difference) of random variables:

where σk, σN- the average square deviation of the measurement errors of the concentration of moisture collected in the k-th and N-th point, respectively;

ρkNthe correlation coefficient between the random components of the error εkand εN.

The measurement results from all the sampling points obtained by one measurement channel in one cycle of the survey, for a short time (1-2 minutes), therefore, the random error of all measurements is very strongly correlated, i.e. ρkN≈1. Given this condition, the last expression is converted to the form

and standard deviation σ [∆Fk(i)] finally still

Considering the fact that the average RMS errors are single-channel measurements, the difference between them is close to zero. Therefore, the sensitivity and reliability of the data on the rate of change of the concentration of moisture in the gas is provided at small increments of absolute values of vlagosoderzhaniya.

If error, for example, hygrometer "Wave - 2M" equal to 2%, the error difference between two consecutive measurements with an interval of 2 minutes is a hundred times smaller.

This fact, put in the basis of the proposed method of protection circuits of the generator allows stovern to detect small changes in the concentration of moisture in the working volume of the generator rather crude devices. And the definition of slew rate concentration provides sufficient and reliable information for classification reason for the increase in moisture and make an informed decision about entering into force reserve equipment gas system generator or emergency output of the turbogenerator of work.

SOURCES of INFORMATION

1. Theoretical fundamentals of heat. Thermal engineering experiment.: The Handbook. / Under the General Ed. Corr.-Corr. USSR Waheguru, Vimsatika. - M.: Energoatomizdat, 1988, book 2.

2. GOST 533-2000 (IEC 34-3-88) interstate standard.

Rotating electrical machines. Turbogenerators. General technical conditions.

3. Alekseev B.A. Definition of States (diagnosis) of large turbogenerators. - M.: Publishing house SC ENES", 2001.

4. RD 153-34.0-45.512-97. Standard instruction manual casamassina system hydrogen cooled generators. Approved by the Department of science and technology of RAO "UES of Russia" 18.06.1997,

5. Description of the invention to the patent of Russian Federation №2066910, CL NN 7/06. The way the relay protection circuit generator voltage generator-transformer with direct water cooling and device for its implementation.

6. Instruction manual turbine generator TW-800-2UZ. Approved by the chief engineer of JSC "Ryazan GRES 18.10.2007,

1. Way protection circuits generators is water cooled, including the measurement of gas moisture in N sampling points of gas from the volume of the generator, characterized in that the measurement of humidity in N sampling points of the gas is realized by one meter in series, from the results of the current measurements in the N-1 sampling point is deducted from the value of the humidity in the N-th point selection obviously most of the dry gas and the rate of change of the differential data is judged emergency water leaks.

2. The method according to claim 1, characterized in that each measurement cycle begins with the sampling point obviously the most dry gas.



 

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